So called dimension lumber is a common commodity. Dimension lumber is formed by cutting lumber pieces from a log to rough cut dimensions and then removing final stock to reduce the lumber pieces to standard cross-sectional dimensions. The dimensioned lumber stock is then typically cut to one of many standard lengths, for example, stud length, 8 foot, 10 foot, 12 foot, etc. to form finished lumber pieces. The final stock removal from the main longitudinal surfaces is typically done by a planer which involves the use of rotary cutting heads as is well known in the art. Rough cut lumber is supplied to a board finishing line that reduces the rough cut transverse dimensions to the final transverse dimensions, and then through a series of steps to a length cutting apparatus that cuts the semi-finished lumber pieces to length to form finished lumber pieces. Various processing stations are involved in the production line and are connected by conveyor systems.
To be efficient, such processing lines run the lumber pieces through at high speeds and through-put rates. The lumber pieces are slowed down from their high speeds through the stock removal step, particularly prior to reaching the grader, for grading and subsequent length trimming and sorting. Lumber is graded into various grades which grades may be relatively arbitrary or subjective or by a recognized standard. For example, five grades of wood may be provided wherein the grades are determined by the quality of the wood, e.g., the number of knots, the surface finish, grain, etc. One grade of wood is referred to as construction grade. Much dimension lumber is used in construction and has standard cross-sectional dimensions, for example so-called 2×4's, 2×6's, etc. Dimension lumber comes in standard lengths, for example, stud length, 8 foot, 10 foot, 12 foot, 14 foot, etc., up to and even sometimes exceeding 24 feet in length. Some lines are built to handle boards 30 feet and even longer. Longer lengths may be provided by joining multiple pieces of short dimension lumber together, for example, with glued finger joints.
In some processes, the cross-sectional dimensioning of the lumber pieces is done at very high movement speeds, for example, up to 4000 feet per minute through a stock removal device such as a planer. The dimensioned pieces are then removed from the stock removal device, and transferred to downstream processing equipment, but are first preferably slowed down prior to subsequent processing steps, particularly for grading at a grader station. Typically, a lumber processing line is simultaneously handling a large variety of lumber piece lengths, e.g., up to 24 feet, even though the largest quantity may be in the 8-14 foot length grouping. The grader station needs to be wide enough to accommodate the longest anticipated pieces even though much of the width is not needed all the time leading to operational inefficiency. Other downstream equipment must be equally wide to also handle the longest anticipated lumber pieces. Grading may be done manually by people and/or computer (or machine) vision techniques. The lumber pieces are then configured relative to one another prior to reaching a length trimming apparatus for subsequent trimming to length. The lumber pieces are trimmed to length preferably after the cross-section is dimensioned. One or both ends of a lumber piece may be cut in the length trimming station to obtain the desired length. When the processing system produces various trimmed lengths, e.g., 8, 10, 12 and 14-foot lengths concurrently, the trimmed length lumber pieces are then sorted by length and grade, bundled, bound, and then shipped.
Such lumber processing operations are well known.
However, even though such processing lines are effective, they do have some drawbacks. A particular drawback is that one or more portions of the processing apparatus present bottlenecks to through-put rates of processed lumber pieces. Operational inefficiencies are also encountered because much of the machine is frequently not being used but needs to be available to handle the longer lumber pieces. One significant bottleneck is the grader, particularly when the grader utilizes manual labor to effect grading. In manual grading, people may turn the boards, inspect all four sides (major longitudinal surfaces) and manually mark grade and trimming instruction designations on the board which are then subsequently read by machine vision with each piece of graded lumber's location within the processing system being known, along with its final cut to length. This information facilitates the sorting of the boards after trimming to length by both length and grade. While more people may be used to help speed up grading, there is a limited amount of space at a typical grading station, thereby placing an upper limit on the grading through-put rate. Grading stations are typically designed to simultaneously accommodate a full range of board lengths. To facilitate grading, the boards are aligned along one side of the machine, since, e.g., an 8-foot long board on a 24-foot wide grading station cannot be accessed except on one side of the grading station.
Lumber processing lines are expensive to purchase, to replace and/or modify. They also have an established footprint in a plant which footprint would also be difficult and expensive to change.
Therefore, there is a need to improve the processing of dimension lumber by improving the through-put rate of lumber pieces particularly at the grading station without requiring major changes in the existing equipment or the footprint occupied by the existing equipment to reduce capital expenditure to solve the problem and to allow simple retrofitting of existing lines.